This invention relates to anaerobic digesters.
In a known type of anaerobic digester, the material to be digested is injected at an inlet port or inlet ports and flows to an outlet port, with a residence time between the inlet and outlet of between four days and three weeks while gas is removed from the top of the digester. In a prior art type of this class of anaerobic digester, the material is injected near the center of the fluid at a temperature cooler than the temperature within the digester and removed through another pipe at the outlet.
The prior art digesters of this type have a disadvantage in that the newly entering material tends to fall to the bottom and then rise as it is warmed, causing an increase in sludge at the surface and under some circumstances a flow back toward the inlet of some sludge at the surface.
Certain of the prior art digesters are concrete structures, recessed into the ground as prefabricated units or constructed on site. Such structures have the disadvantage of being too expensive for relatively small digesters. It has been proposed that plastic tubing be used, but the use of such tubing has the disadvantage of making it difficult to gain access to the flow path for maintenance or observation.